Oligosaccharides form an important group of polymeric carbohydrate that is extensively used as food additives and nutritional supplements. Oligosaccharides are composed of monomeric sugar units linked by glycosidic bond with a degree of polymerization 2 to 10. They are hydrolyzed readily by acid or enzyme to their respective monomeric sugar constituents. Oligosaccharides provide several health benefits which make them useful as food additives. Physiochemical and physiological property of the oligosaccharide vary depending on the mixture of oligosaccharide produced. Oligosaccharides having degree of polymerization 3 to 10 are prebiotic, with low colorific value, and are used as soluble dietary fiber.
Oligosaccharides are produced either by non-enzymatic methods or enzymatic methods. Non-enzymatic methods involve extraction of oligosaccharides from natural source and chemical synthesis using monosaccharides or disaccharides as starting material. Enzymatic methods involve synthesis of oligosaccharides using glycosidases and glycotransferases as catalyst and enzymatic hydrolysis of polysaccharides into oligosaccharides.
Production of oligosaccharides from agri-waste leads to exploitation of agri-waste, such as shell, bran, husk, hull, cob and oilseed meal, which is otherwise used as animal feed. These wastes contain majorly of cellulose and hemicellulose along with proteins, phytochemicals and lignin. All these constituents are arranged in a complex polymeric matrix which prevents accessibility of polysaccharides for hydrolysis. However, thermo-chemical treatment provides amenable biomass which when further subjected to controlled enzymatic hydrolysis helps to achieve a high yield of oligosaccharides of desired properties. Production of bioactive oligosaccharides from easily available agri-waste gives promising benefits to agro-based industry.
The prior arts provide various methods for manufacture of oligosaccharides from biomass. These methods involve the use of either microbial cell or enzymes for breakdown of biomass into oligosaccharides. However, the methods described in the prior art require specific enzymes for production of oligosaccharides. The methods described in the prior art produce mixture of oligosaccharide which require downstream operations for its purification, thereby increasing the cost of production.
U.S. Pat. No. 5,246,840 discloses a method for synthesis of oligosaccharides by using glycosidases and glycotransferases as catalysts. Oligosaccharide synthesis was achieved by combining glycosidase catalyzed synthesis of shorter oligosaccharides with glycotransferase catalyzed synthesis of higher oligosaccharides.
U.S. Pat. No. 4,677,198 discloses a process for the preparation of oligosaccharides-containing products from biomass, which provides use of hydrochloric acid for partial hydrolysis of biomass to easily fermentable oligosaccharides containing products and easy recovery of acid. These oligosaccharides were further subjected to fermentation for preparation of products like ethanol.
JP2008136376 describes a process for production of acidic xylooligosaccharides, from wheat/rice bran. In this process, acidic xylooligosaccharides was obtained after hot water treatment, under acidic condition of pH range of 1.0-4.0, or under alkaline condition of pH range of 9.0-13.0 of wheat bran or rice bran at temperature in between 100-150° C. followed by ion exchange treatment. The process yields acidic xylooligosaccharides, having degree of polymerization 2-5.
EP1304412 discloses a method for production of xylooligosaccharides from lignocellulosic pulp using enzymes, which comprises enzymatic hydrolysis of lignocellulose pulp using hemicellulases followed by membrane separation to obtain non permeate fraction with high concentration of xylooligosaccharides-lignin mixture which was further treated to recover xylooligosaccharides.
U.S. Pat. No. 4,908,311 discloses a method for cellooligosaccharide from cellulose-base substance by enzymes. Cellulase produced by microorganism belonging to the Genus Cellvibrio was used as catalyst for enzymatic break down of cellulose material. Enzymatic hydrolysis in combination with membrane filtration reactor helps in removal of inhibitors and accumulation of cellooligosaccharides.
U.S. Pat. No. 7,947,656 describe a process for production of cellooligosaccharides by enzymatically decomposing a cellulose material. The process consisting of breakdown of cellulosic material, having an average degree of polymerization not greater than 700 and average particle size not greater than 100, using cellulase to selectively produce cellooligosaccharides.
US20110020498 discloses a process for preparation of (arabino) xylan oligosaccharides from wheat bran using endoxylanase. Further process includes destarching, deproteination followed by enzyme hydrolysis with endoxylanase from Bacillus subtilis. The purification of (arabino) xylan oligosaccharide was done with ion exchange chromatography. This process was produced (arabino) xylan oligosaccharides with average degree of polymerization between 4 and 10 with average degree of arabinose substitution between 0.15 and 0.35 and has good organoleptic and color properties.
US20100021975 describes a process for production of xylooligosaccharides by cold caustic extraction of pulp obtained after cooking process. The process involves cold caustic extraction of xylan followed by membrane separation process to obtain xylan enrich retentate. This xylan fraction is further processed by hydro-thermolysis and enzymatic hydrolysis for conversion of xylan into xylooligosaccharides.
US20090062232 describes method for preparation of high purity xylooligosaccharides from plant material comprising of alkali treatment, pressure and heat treatment of plant material followed by solid-liquid separation. Solid residue was further subjected to enzyme hydrolysis using xylanases. Crude saccharide extract was concentrated followed by the desalting and active carbon treatment to produce high purity xylooligosaccharides composition free from UV absorbing substances and coloring impurities.
US20110244073 describes a method for preparation of arabinoxylan and arabinoxylo-oligosaccharides. The process for preparation of water soluble arabinoxylan includes hot water treatment of water-unextracted arabinoxylan in the presence of thermostable amylase followed by addition of ethanol to final concentration of 70/30 (v/v) ethanol/water after cooling to 70° C.
U.S. Pat. No. 5,633,032 describes a method for preparation of cereal extracts. In this process cereal bran material obtained from milling was subjected to alkali treatment at temperature 70-80° C. followed by solid-liquid separation. Insoluble residue was again treated with alkaline hydrogen peroxide at 70-80° C. followed by solid-liquid separation. Soluble fraction was then spray dried and used as adhesive and thickening agent.
US20120231147 relates to the production of xylooligosaccharides by auto-hydrolysis of grain products. In this process corn fiber separated was from distillers and the dried grains with solubles (DDGS) was subjected to auto-hydrolysis using deionized water at temperature in the range of 140-220° C. to give an extract containing xylooligosaccharides, monosaccharides and acid. This extract was further hydrolyzed using acid to form monosaccharides.
US20120232264 describes a two-step process for biomass treatment. The first step of process involves treatment of biomass with pressurized water at a temperature between 100 to 200° C. to release hemicellulose as xylooligosaccharides. In the second step, insoluble residue was again treated with pressurized water at a temperature of 200 to 300° C. to obtain cellooligosaccharides. Thus the obtained xylooligosaccharides and cellooligosaccharides were further hydrolyzed using solid acid catalyst to generate xylose and glucose respectively.
US20120115192 provides a process of production of fermentable sugars from biomass using multi-step multi-enzyme system. In this process, biomass was first treated with 5% to 10% w/v alkali at temperature ranging from 50 to 200° C. under 1 to 20 bar pressure for removal of hemicellulose leaving behind cellulose residue. Furthermore hemicellulose was precipitate by addition of ethanol solvent. Thus, precipitated hemicellulose and cellulose were then enzymatically hydrolyzed using xylanases and cellulases preparation for production of fermentable sugars.
The above described methods produce either xylooligosaccharides or cellooligosaccharides from biomass using enzymatic and chemical methods. Enzymatic methods involve treatment of biomass with cell-wall modifying enzymes such as amylase, glucoamylase, protease, pullunase and lipase for removal of starch and non-carbohydrate components. Thereafter, the carbohydrate contained in the biomass is hydrolyzed using either xylanase or cellulase to produce xylooligosaccharides or cellooligosaccharides respectively. The two step process described in the prior art increases the overall cost of production as it requires chemical pretreatments for polysaccharide extraction followed by its hydrolysis into oligosaccharides using specific enzymes.